Available

Issued

Submitted

Other

Subject

Type

Metadata

Abstract

Abstract
In oil sands mining operations, water is an essential ingredient of the extraction process, however, it becomes contaminated through contact with bitumen at high temperature, and ultimately ends up in tailings ponds. Through repeated recycling of produced water, concentration of contaminants increases over time. Similar contamination of water occurs in oil sands in-situ recovery operations where high pressure saturated steam is commonly used to contact bitumen in the reservoir. Some of the most troublesome of the contaminants found in the produced water are naphthenic acids, naturally occurring compounds in bitumen. Naphthenic acids are a mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids. Studies have shown that the concentration of naphthenic acids in tailings ponds and produced water from in-situ recovery operations is substantial and that they are corrosive and toxic making their removal from water crucially important. In addition, the presence of dissolved organic compounds in tailings pond water is thought to contribute, through bacterial degradation, to the emission of methane from the ponds into the atmosphere, methane being one of the most potent greenhouse gasses.
Several methods have been reported for removing naphthenic acids from water, such as catalytic reactions, membrane separation, microbial reaction and adsorption. In this work, the removal of naphthenic acids by adsorption using activated carbon was investigated since among a variety of adsorbents, activated carbon is considered to be highly effective. Sawdust was selected as the raw material for producing activated carbon due to its abundance and anticipated low cost. In addition, biomass-based activated carbon can play a role as a carbon sink so it can contribute to reducing the carbon emission footprint of oil sands operations.
The methods employed in this work for producing activated carbon from sawdust were physical activation using carbon dioxide (CO2) and chemical activation using phosphoric acid (H3PO4). For comparison, a commercially activated carbon was also used. The physically activated carbons were found to have lower surface area than the chemically activated carbon. In biochar production, the carbonization temperature showed the strongest effect on yield of produced biochars. Heating rate and activation time were ranked second and third respectively. Generally a yield of around 20-30% is expected during the production of biochar from sawdust. During physical activation of the biochar, activation temperature was shown to be the most important factor affecting the surface area of the activated carbon and an optimum activation temperature of 825 °C was determined. The Langmuir Isotherm provided the best fit of experimental data for the physically activated carbons suggesting mono-layer adsorption. The Sip isotherm provided the best fit to the data for the chemically activated carbon.
Naphthenic acid adsorption tests were done at different initial concentrations, in order to obtain the isotherm for each activated carbon. In the adsorption tests, the chemically activated carbon showed greater uptake of naphthenic acid, which can be attributed to the higher surface area and increased mesopore size. It was observed that both the chemically and physically activated carbons had greater naphthenic acid uptake than the commercially activated carbon. A removal range between 60-90% of total organic carbon (TOC) was achieved using ACs produced in this study for different concentrations of contaminants